This project is concerned with the appearance and accumulation of myosin isoenzymes during the early embryonic development of the heart and how these are correlated with morphogenetic changes observed during this time period. By better understanding what events are occurring at the molecular level during early development and relating these to observed morphogenetic hcanges, we should be able to elucidate how genes control normal organ shape development. We intend to attack this problem from several perspectives. Initially, the distribution of myosin isoenzymes in the heart-forming and cardiac regions of chick embryos will be determined by using antibodies to specific myosin species. By interfering at the molecular level with myosin expression (using the drug diazepam to attempt to inhibit myosin heavy chain synthesis), we will correlate observed morphological abnormalities produced by diazepam in developing hearts with specific molecular events, as well as changes at the cellular, ultrastructural, and organ levels. Thus, by combining several types of approach to a single problem, we would hope to gain some insight into how normal, and perhaps, abnormal cardiogenesis occurs and is regulated.